Process of selectively refining petroleum oils



Patented Sept. 24, 194

Process 0F SELECTIVELYBEFINING.

PETROLEUM. oILs Arthur w. Hixson, Leonia, N. .L, and Ralph Miller, I New York, N. Y., assignors to The Chemical Foundation, Incorporated, a corporation of Delaware No Drawing. Application December 17, 1936,

- Serial No. 116,348

8 Claims.

This invention relates to the fractionation of oils, more particularly to the separation of petroleum oil into a series of desirable, valuable fractions by a special system of fractional extraction.

Petroleum oil, as is known, comprises essen tially a complex mixture of different homologous series or groups of hydrocarbons, such as paraflinic, naphthenic, and aromatic constituents. When petroleum oil is separated into the commercially useful fractions, such for example as the gas oil, lube oil, and fuel oil fractions, the same generalcomplexity still obtains, although the respective percentages of the diiferent groups 5 in such commercial fractions may vary. Thus a typical, relatively high boiling range distillate. having the characteristics of lubricating oil, contains paraifinic, naphthenic and aromatic constituents and some asphalt. The respective proportions of such constituents depend upon the 1 type or source of the crude 011. Thus Pennsylvania. oil contains little or no asphalt and a relatively small amount of aromatics. The Coastal oil, conversely, has a relatively high percentage of asphalt and aromatics. Mid-Continent oil is approximately an intermediate of these-two, containing appreciable amounts of asphalt and of aromatics in addition to the paraffinic and naphthenic constituents. It is well recognized that a paraffinoil fraction possesses the best lubricating properties and it is for this reason that the Pennsylvania base oil constitutes the accepted standard.

It is also well recognized that the paraflinicity "of a given lubricating oil fraction may be increased by treating such fraction to remove naphthenic constituents. Hence it has been proposed to improve the lubricating qualities of a given oil by treating such oil with solvents which have a preferential affinity for the nonparaffinic constituents. Such processes consist essentially in contacting a given lube stock with a solvent mixture, at a temperature sufliciently high to insure miscibility of the solvent with the oil, and subsequently in cooling the mass to a I temperature that will .insure immiscibility. In

these circumstances stratification into two layers obtains; one layer comprises the solvent with its dissolvednaphthenic, aromatic and asphalt constituents, and the other layer comprises largely the paraflinic constituents of the starting material. The two fractions are then subjected to distillation to remove the contained solvent. Modifications of such extraction processes include the use of dual solvents, the retreatment of the rafiinate with the original solvent or a. specifically different solvent to further refine it, and the like. The desideratum in all such prior methods, however, has been to enhance the selectivity of the fractionation for the purpose of 6 securing the maximum yield of the high viscosity index parafllnic fraction.

To render such proces'ses commercially feasible it is necessary to separate and recover the solvent which is employed. This is usually done, as 10' noted, by vacuum distillation. The residual naphthenic oil or extract is thus more naphthenic than the original oil which was subjected to the treatment. This extract, however, because of the relatively large percentage of contained 15 asphalt, is a viscous, tacky, black, tar-like product. The quantity of the asphalt in a given extract will, of course, vary depending upon the type of lubricating oil stock treated. It is greatest in the extract produced from the asphaltic 20' base oils. Such extract, although relatively free from paraffinic constituents, does contain an appreciable quantity of potentially valuable oil. However, due to the large percentage of asphalt contained in the extract, such fraction is prac- E tically useful only as a cracking stock since it is too diflicult and expensive to separate the oil from a fraction of a high asphalt concentration.

If the oil which is to be treated is not deasphalted and contains an appreciable amount 30 of asphalt, solvent refining will not'remove the asphalt from the paraflin fractions, although such asphalt will be concentrated, to a considerable degree, in the extract layer. It is of course possible to remove the asphalt from the 35.

oil prior to solvent extraction. If the oil is deasphalted to a certain extent, selective solvents will then dissolve the residual asphalt, the color bodies, the aromatic and naphthenic constituents, but will not dissolve the paraflinic hydro- 4.3 carbons.

The typical process of solvent extraction is, in effect, a method of separating various constituents present in the oil. If, as is usually the case, the extraction process is operated to pro- 415 duce a raflinate of high viscosity index from an initial or starting material having but a small percentage of high viscosity index oil, it is clear. that the yield 0f"'the paraflinic'fraction must necessarily be low. In these circumstances, be- 50 cause of the characteristics of the extract, the remainder of the oil is vemployable only for cracking purposes.

The present invention, as will more fully appear, is based on the concept of recovering the 51;

fractions and a residuum of a high asphalt concentration. The first lubricating oil fraction would comprise a valuable, high viscosity index railfinate of excellent lubricating properties. The second novel, recoverable fraction would constitute a marketable lubricating oil fraction of lower viscosity ,index, comprised largely of naphthenic and aromatic hydrocarbons substantially free from asphalt. Finally, the third fraction would comprise an oil of a high asphalt concentrationwhich, being less refractory than the extract, constitutes a good low temperature cracking stocks Again this third fraction may suitably be treated, by methods known to those skilled in the art, to produce valuable products, such as road oils, binders, mastics, and the like.

It has been fpund that such advantages may be attained and the enumerated novel results, secured by a method, which is not only simple and effective but which also mayreadily be correlated with present methods of solvent extraction.

' A major object of the present invention is to devise a method of producing commercially valuable fractions from petroleum oils.

Another object is to provide a method of separating and recovering the more valuable constituents of the naphthenic-like extracts from the less valuable constituents. v

Yet another object is to produce a novel type of petroleum cracking stock.

An additional object is to devise an effective method of selectively extracting parafflnic and naphthenic fractions from an asphalt-containing oil. I

With these and other equally important and related objects in view, the invention comprehends the concept of subjecting a natural or pyrogenetically produced petroleum oil fraction to a special type of sequential, selective solvent extraction to recover therefrom a fraction of higher paraflinicity than the original oil, a second. oil fraction of higher naphthenicity than the original oil, and a residual'fractlon in which'the.

asphalt of the starting material is largely concentrated. In sharp contradistinction to priorart methods, in which the original oil was separated into a rafiinate and a cracking stock of low value, the present method insures the recovery of a number of valuable fractions. 'Thus.operating under the present method there is produced an excellent lubricating fraction of optimum paraffinicity, a valuable naphthenic lubricant substantially free from tarry matter, and a viscous residual oil of high asphalt concentration.-

. The present invention is, in a sense, an extension of the discovery explained in copending application Serial No. 60,634, filed January 24, 1936,

now Patent No. 2,143,415, dated January 10, 1939, and to this degree the presentv application is a continuation in part of the prior application. As-

explained in that application, a certain class of solvents possess a striking preferential solvent action on the non-paraflinic consituents of a mixed base oil. It was further explained that the high selectivity of these solvents is due to the unequal distribution of the electronic charges of the molecule, i. e., its polar characteristics, and that theefiective index of selectivity ofa solvent is its dipole moment. It was additionally pointed out that solvents which were characterized by a high dipole moment and which also possessed the other desirable characteristics, such as low melting point, miscibility at elevated temperatures, -immiscibility at lower temperatures, etc., served .most effectively as single solvents for the separation and recovery of rafiinate.

It is now found that this characteristic of optimum selectivity of certain solvents for the non-paraflln-ic constituents renders them peculiarly useful for the production of substantially asphalt-free naphthenic-like. oil fractions. This result can be achieved by treating a solution of the non-parafiinic constituents in a highly selective solvent with a second solvent which functions to extract a certain percentage of the lighter oil from the selective solvent, leaving in,

the selective solvent phasethe heavier asphalt constituents. In the preferred embodiment of the present invention the first solvent is preferably one which is characterized by'a high selectivity and relatively low solubility, such for example as ortho-nitroanisole and ortho-methyoxybenzonitrile. As will appear more fully hereinafter however, the present invention is not limited to these particular solvents but is available for employment with any solvent which possesses a'marked selectivity for the naphthe'nic fractions and which is immiscible with the clarifying solvent.

In order; to insure the improved results mentioned it will be appreciated that the second or clarifying solvent must possess certain characteristics. It must be a solvent for oil although, as will be understood, it need not be selective with respect to' paraflinic and naphthenic oils. It

must of course be immiscible with the selective naphthenic solvent at the temperature at which stratification is to be eflected, and preferably should be immiscible with the selective solvent.

even at relatively elevated temperatures. It 'must be amenable to use with the particular selective naphthenic solvent employed. The clarifying solvent should also be of such a character as to beemployable without the use of expensive equipment.

A typical illustrative solvent of this type which effectively fulfills the enumerated prerequisites is tri-amylamine. This alkyl amine is insoluble in water; it has a marked solubility for oil at any temperature; it has adistillation range of 230 C. to 260 0., and a specific gravity of .7937 at 20 C. It dissolves orthonitroanisole, one of the preferred solvents, only very slightly at room temperature and is completely miscible with orthonitroanisole at C. This, as will be appreciated, is a wide permissive operating range. Since the clarifying solvent may be contactedwith the selective solvent-naphthenic oil phase at any temperature below this miscibility temperature, the solubility of the tri-amyline for theoil bodies can be modified to a considerable degree to thus control the aniount and/or quality of the oil removed from the selective solvent phase.

As will be seen more fully hereinafter, the majoa' desirable characteristics of the selective solvent are maximum selectivity and relatively low solubility. The salient characteristics upon which the choice of the clarifying solvent is based are, as noted, a marked solubility for oil bodies at any temperature, relatively low selectivity and a high temperature of miscibility with the selective solvent.

Tri-amylamine is peculiarly effective for the purposes of the present invention and serves well to illustrate the principles involved, as is shown by the following treatment.

A given quantity of a mixed base oil was treated with 246% by weight of ortho-nitroanisole in a continuous, countercurrent extraction system. The mass was heated to the miscibility temperature, as explained in the copending application referred to, and the temperature at the solvent outlet of the system was held at approximately 20 C. Under these conditions, upon analysis it was found that 29% of the original oil was removed in the solvent phase, the remainder constitutinga high viscosity index raffinate. The solvent phase was then treated with tri-amyla mine in the same countercurrent system in which the temperature of the mass was maintained at substantially 26 C. The amount of tri-amylamine used was 83% by weight of the original oil. The tri-amylamine fraction was segregated from the ortho-nitroanisole fraction and was subjected to vacuum distillation. It was found that a small amount of ortho-nitroanisole was recovered in the distillate. Upon analysis it was found that 56% of the oil originally dissolved in the ortho-nitroanisole was solubilized and extracted by the tri-amylamine.

The residual fraction, i. e., the ortho-nitroanisole and its dissolved oil, was then subjected to vacuum distillation. to recover the solvent. wasfound, similarly, that a slight amount of the tri-amylamine was-contained in the ortho-nitroanisole condensate. The extract remaining after the distillation and removal of the selective solvent was a highly viscous, tacky, tarry mass.

Under the conditions of the treament, therefore, the original oil was fractionated into a typical raflinate, a second clarified fraction, i. e. the extract from the tri-amylamine phase, and a highly viscous residue. The raflinate constituted approximately 71% of the original charge: the

clarified tri-amylamine extract substantially 16% of the original charge, while but approximately 12% was recovered in the viscous residue.

The effectiveness of the treatment in separating the constituents of the original oil is seen from a comparison of the tri-amylamine extract and the ortho-nitroanisole extract. The original oil had a viscosity of 265'Saybolt seconds at 100 F. and 46.6 Saybolt seconds at 210 F. The triamylamine extract had a viscosity of 555 Saybolt seconds at 100 F. and 55.3 Saybolt seconds at 210 F., and a viscosity index of '9. The heavy residuum, on the other hand, had a viscosity of 115 Saybolt seconds at 210 F.

It is to be observed that the clarified naphthenic fraction, or tri-amylamine extract, although of a low viscosity index, is nevertheless a commercially useful fraction and employable, for

example, as a medium quality light lubricant.

The essential features of the improved method of fractional separation of oil therefore comprises, extracting a given mixed base oil fraction with a solvent which has a preferential affinity for the non-paraflim'c bodies, then further treating the solvent phase with a clarifying oil solvent, at any temperature at which the two solvents will not form a homogeneous liquid phase so as to establish stratification of the respective solvents and their dissolved constituents. The second extrac-' tion, as will be appreciated, may be carried out at any temperature below the miscibility temperature of the two solvents chosen. Other things being equal, the higher the miscibility temperature of the two solvents and the greater the selectivity of the selective solvent, the greater will be the permissive thermal operative range and the greater will be the corresponding permissive variation of the characteristics of the clarified extract. Again, as will be understood, the lower the solubility of asolvent of given selectivity, the greater will be the quantity of oil extracted by the clarifying solvent.

The choice of the selective and clarifying solvents, as is understood by those skilled in the art, will be determined by a number of factors, such as; the character of the stock to be treated, the quantity of and characteristics desired in the ultimate fractions, the type of plant equipment available, and the like.

The process is, of course, operable with a relatively wide rangeof selective solvents, that is. to say the invention is by no means limited to the use of the highly selective solvents enumerated. Thus, for the selective solvent utilized for the preliminary extraction there may be employed, in addition to ortho-nitroanisole and ortho-methyoxybenzonitrile, other solvents of marked selectivity, such as furfural, aniline'and the like. As explained, the particular clarifying solvent which is chosen should be correlated with the selective solvent, and upon the basis of the factors given the optimum clarifying solvent for any given operation can readily be determined.

With highly selective solvents, such as orthonitroanisole, the quality of raffinate that may be produced, when utilizing a given oil-solvent ratio, depends essentially on the oil outlet temperature of the system. Similarly, the yield or quantity of the rafiinate depends essentially on the solvent outlet temperature. The characteristics of the second fraction, for any given clarifying solvent and operating conditions, will thus be governed to a considerable degree by the extraction conditions obtaining in the first refining stage.

When refining a Mid-Continent oil, for example, by solvent extraction with selective solvents, a relatively large sacrifice in yield must be made in order to secure a small increase in viscosity index when the viscosity index of the rafiinate is about 90. Generally when a single selective solvent is employed for the fractionation, it is not usuallyeconomical to make too great a sacrifice in yield in order to obtain the highest viscosity index 011. The operations conducted heretofore have, therefore, necessarily been a compromise between these factors. ily be appreciated that under the present method, assuring as it does the production of a second valuable product, this sacrifice in yield can more readily be made, thus insuring'recovery of. the

,optimum quality of lubricating stock, coupled with the maximum recovery of valuable oil fractions.

It is to be understood that the operations described herein need not be carried out under conditions controlled to insure a substantially quantitative separation of the paraiiinic constituents in the first extraction stage. If the selective solvent extract does contain some amount of parafiinic oil, upon the'addition of th second solvent which is immiscible with the selective solvent, the residual parafllnic constituents will largely be naphthenic constituents.

taken up in the second solvent because of the greater aflinity of the selective solvent for the In other words, the second solvent displaces the remaining parafiinic constituents from the selective solvent phase.

The principles of the invention may be eifected by a number of specifically different methods and by utilizing diiierent types of apparatus. In a typical commercial embodiment, for example, a given oil fraction may be contacted with the selective solvent, such as ortho-nitroanisole, in a suitable batch or continuous countercurrent/ system, as more particularly explained in Patent No. 2,143,415. If a light oil were to be refined, the first extraction step may be operated with an oil outlet temperature inthe approximate range of from about 115 C. to 120 C? more or less. The solvent outlet temperature may be maintained at approximately 60 C. These temperatures, as is known, will be controlled depending upon .the

quality and yield of raifinate desired. After stratification and separation of the ramnate in any suitable manner, the solvent phase may, if desired, be cooled further to insure the separation of an additional quantity oi the raffinate.

The cold solvent phase may then be contacted with a suitable second solvent, such as tri-amylamine, in a second batch or countercurrent system. In this manner the immiscible second solvent extracts from the selective solvent-oil phase a considerable fraction of the dissolved oil'. The temperature at which the second extraction is effected may be controlled at any degree below the miscibility temperature of the selective solvent and the clarifying solvent. The yield and quality of oil removed in the clarifying solvent phase can therefore be controlled within relatively wide ranges.

The viscous, residual fraction produced in the system may be utilized as a cracking stock. Since this stock contains a relatively high percentage of the heavy hydrocarbons, cracking may be carried out at relatively low temperatures. This fraction may also be suitably processed as by steam distillation, air blowing and the like, to produce valuable, marketable asphaltic products.

While the improved method of treating petroleum oil has been described as being particularly applicable to the refining of lubricating oil fractions, it is to be understood that it is notlimited to this particular stock. The principles of the invention may be invoked in any circumstance where it is desired to secure the selective recovery of similar petroleumoil constituents from any initial mixtures thereof. Hence, while preferred modifications of the invention have been -de-- scribed, it is to be understood that these are given to illustrate the principles involved and not as defining the exclusive methods of eifectuating these principles.

We claim:

1. A process of refining petroleum oils containing parafiinic and naphthenic constituents which comprises, contacting the oil with a solvent which has a preferential affinity for the non-paramnic constituents of theoil; separating the solvent with its dissolved naphthenic" constituents from the undissolved oil constituents; then contacting the separated solvent-oil phase with a second oil solvent which is substantially immiscible with the first solvent to largely displace the naphthenic constituents from the first solvent and establish twoseparate solvent-oil phases, and recovering the oil fractions from each 011 phase.

2. In the solvent refining of petroleum oil in a and a preferential .afiinity for naphthenic constituents as compared to the selective solvent) and which is completely miscible with the first solvent only at a a predetermined elevated temperature. and regulating the temperature during such contact to a degree below said miscibility temperature to establish two separate solvent-oil phases, in each of which phases predetermined diflerential oil constituents are dissolved.

3. A process of refining petroleum hydrocarbons which comprises contacting a petroleum base oil containing parafilnic and naphthenic constituents with a polar solvent having a dipole moment above 4.5 D; stratifying the mass into a ramnate and a solvent phase in which the naphthenic constituents are largely dissolved; separating the solvent phase from the oil phase and then treating the solvent phase, at relatively low temperatures, with a second oil solvent which is characterized by a substantial immiscibility with said polar solvent at said temperatures and a greater selectivity for naphthenic constituents than said polar solvent. A

4. A process of refining petroleum oils containing paramnic and non-parafiinic constituents which comprises, contacting the oil with a single solvent which is highly selective to the nonparaffinic constituents of the oil, separating the solvent with its dissolved oil constituents from the undissolved constituents; then contacting the separated solvent-oil phasewith a second oil solvent which is substantially immiscible with the selective solvent and which has a greater solubility for naphthenic constituents than the said single solvent, to establish 'two separate solventoil phases, and recovering the oil fractions from each oil phase.

5. A process of refining petroleum oils containing parafinic and non-paraflinic constituents which comprises, treating the oil with a highly se- .lective single solvent which has a preferential affinity for the non-parafilnic constituents, to

petroleum oil with ortho-methyoxybenzonitrile at a temperature above the miscibility temperature of the oil and the solvent; stratifying the mass into an oil phase and a solvent phase; separating the solvent phase from the oil phase; cooling the solvent-oil phase to remove additional quantities,

of oil therefrom; and then treating the solvent phase, at relatively low temperatures, with a' second oil solvent which is characterized by a sub- 'stantial immiscibility with ortho-methyozwbenzonitrile at said low temperature.

contain parafllnic and non-paramnic constituents including naphthenic and asphalt bodies which comprises, contacting the oil with ortho-methyoxybenzonitrile at temperatures above the miscibility temperature, cooling the mass to stratify it into an oil phase and a solvent phase; separating the solvent phase with its dissolved oil from the oil phase, and treating such solvent phase with triamylamine' under conditions regulated to preferentially extract naphthenic oil constituents from 10 the ortho methyoxybenzonitrile phase.

ARTHUR w. mxson. RALPH MILLER. 

